Unsymmetrical perylene dimers in electrophotography

ABSTRACT

Photoconductive imaging members comprised of unsymmetrical dimeric perylene as a charge generator, wherein said perylene is of the following formula ##STR1## wherein R is hydrogen, alkyl, cycloalkyl, substituted alkyl, aryl, substituted aryl, aralkyl or substituted aralkyl group, and X-Y is an unsymmetrical bridging moiety of alkylene, substituted alkylene, arylene, substituted arylene, aralkylene or substituted aralkylene.

PENDING APPLICATION

There is illustrated in copending application U.S. Ser. No. 700,326, thedisclosure of which is totally incorporated herein by reference,photoconductive imaging members with symmetrical dimeric perylenes.

BACKGROUND OF THE INVENTION

The present invention is directed generally to dimeric perylenepigments, and more specifically, to unsymmetrical perylene bisimidedimers of the formula ##STR2## wherein R is hydrogen, alkyl, cycloalkyl,substituted alkyl, aryl, substituted aryl, aralkyl, substituted aralkyl,and the like, and X-Y, which X-Y can be represented by a single Z,represents an unsymmetrical bridging moiety such as alkylene,substituted alkylene, arylene, substituted arylene, aralkylene orsubstituted aralkylene. Alkyl includes linear and branched componentswith, for example, from 1 to about 25, and preferably from 1 to about 10carbon atoms, such as methyl, ethyl, propyl, butyl, pentyl, heptyl,octyl, decyl, and the like. Cycloalkyl includes homologous rings from,for example, cyclopropane to cyclododecane. Substituted alkyl groupscontain substituents such as hydroxy, alkoxy, carboxy, cyano,dialkylamino and the like. Aryl includes components with, for example,from 6 to about 24 carbon atoms such as phenyl, naphthyl, biphenyl,terphenyl and the like. Substituted aryl groups contain, for example,one to five substituents such as alkyl like methyl, or tertiary-butyl,halogen (fluoro, chloro, bromo, and iodo), hydroxy, alkoxy like methoxy,nitro, cyano and dimethylamino. Aralkyl includes components with from 7to about 24 carbon atoms such as benzyl, phenethyl, fluorenyl and thelike. Substituted aralkyl groups can contain the same substituents asthe aforementioned aryl groups, and more specifically, for example,methyl, tertiary-butyl, halogen, hydroxy, methoxy, nitro anddialkylamino.

Unsymmetrical bridging groups X-Y, (Z) include alkylene such as1,2-propylene, 1-methyl-1,3-propylene, 1-ethyl-1,3-propylene,1-methyl-1,4-tetramethylene, 2-methyl-1,4-tetramethylene,1-methyl-1,5-pentamethylene, 2-methyl-1,5-pentamethylene and higherunsymmetric alkylene groups with up to about 20 carbon atoms.Unsymmetric substituted alkylenes include, for example,3-hydroxy-1,2-propylene, 2-hydroxy-1,4-tetramethylene,2-methoxy-1,4-tetramethylene, 2-carboxy-1,4-tetramethylene and2-dimethylamino-1,4-tetramethylene. Arylene denotes unsymmetricallysubstituted bridging groups including 2,4-, 2,3'-, 2,4'-, and3,4'-biphenylene, and 1,3-, 1,6- and 1,7-naphthylene. Substitutedarylenes include groups such as 2-chloro-1,4-phenylene,2-methyl-4,4'-biphenylene, N-phenylbenzamide-3,4'-diyl,diphenylsulfone-3,4'-diyl and diphenylether-3,4'-diyl. Aralkyleneincludes benzyl-, phenethyl-, phenylpropyl- and fluorenyl-groups inwhich one perylene bisimide moiety is bonded to the alkyl group and thesecond is bonded to the 2-, 3- or 4-position of the aromatic ring.Substituted aralkylene includes groups of the aforementioned class inwhich substituents such as methyl, tertiary-butyl, halogen (fluoro,chloro, bromo, and iodo), hydroxy, methoxy, nitro, cyano anddimethylamino are attached to the aromatic ring. Examples of theunsymmetrical bridging X-Y or Z groups are illustrated hereinafter.

Embodiments of the present invention include a process for thepreparation of the unsymmetrical perylene bisimide dimers in high yieldand high purity, which process comprises the reaction of preferably atleast two parts of a perylene monoimido anhydride of the followingFormula 2, with an unsymmetrical diamine in a high boiling solvent, suchas N-methylpyrrolidine, and washing the resultant product with hotsolvents to remove residual starting components and other byproducts.

FORMULA 2 Perylene Monoimido Anhydride ##STR3## wherein R represents thegroups or substituents described in Formula 1.

The unsymmetrical perylene dimers illustrated herein can be selected asa photoactive component in photoconductive imaging members used inelectrophotographic printing, organic solar cells and, because of theasymmetry induced by the bridging moiety, they are expected to possessnon-linear optical properties. Moreover, in embodiments theunsymmetrical dimers can be selected as a colorant in polymericcomposite materials such as plastic objects, xerographic toners, and thelike. The perylenes of Formula 1 can be selected, it is believed, as acomponent for solid state devices such as in solar cells, chemicalsensors, electroluminescent devices and non-linear optical devices. Theycan also be used as dispersed colorants for coloration of, for example,plastics.

Important embodiments of the present invention include photoconductiveimaging members comprised of a supporting substrate, a photogeneratinglayer comprised of the perylene dimer pigments illustrated herein ofFormula 1 and a charge transport layer. Furthermore, the perylene dimerpigments are highly colored and can be prepared with a variety of huessuch as orange, red, magenta, maroon, brown, black, greenish black, andthe like depending, for example, on the R and X-Y substituents.

With the present invention in embodiments, photoconductive imagingmembers with the perylene dimer pigments obtained by coupling twoperylene monomers together via an unsymmetrical bridging group (X-Y inFormula 1) enable a number of advantages with respect, for example, tophotoconductive imaging members with monomeric perylene pigments or withsymmetrical dimeric perylene pigments described in U.S. Ser. No.700,326. For example, as indicated hereinafter the dimer of Formula 1,wherein R=n-pentyl and X-Y is 2-methyl-1,5-pentamethylene, possessessubstantially higher photosensitivity than the related monomericperylene pigment typified by a general Formula 3a, with two pentylgroups or the corresponding symmetrical dimer represented by Formula 1wherein R=n-pentyl and X-Y is the symmetrical 1,6-hexamethylene group.

In embodiments, the present invention is directed to photogeneratingpigments comprised of unsymmetrical perylene bisimide dimers.Embodiments of the present invention are directed to an imaging membercomprised of a supporting substrate, a photogenerating layer comprisedof an unsymmetrical perylene dimer of Formula 1 and, more specifically,wherein where R=n-propyl, n-butyl, isobutyl, n-pentyl, 2-methylbutyl,3-methylbutyl, n-hexyl, n-heptyl and n-octyl andX-Y=2-methyl-1,4-tetramethylene, 2-methyl-1,5-pentamethylene,toluene-a-4-diyl, ethylbenzene-b-4-diyl, diphenyl ether-3,4'-diyl andthe like, and a charge, especially hole, transport layer. Morespecifically, the unsymmetrical perylene dimers of the present inventionare comprised of two different perylene bisimide molecules having thesame terminal substituent (R group in Formula 1) wherein the twoperylene moieties are distinguishable by being bonded to different endsof the unsymmetrical --X-Y-- bridging group. The perylenes of thepresent invention can be characterized as having no center of symmetry.Imaging members with the photogenerating pigments of the presentinvention are sensitive to wavelengths of from about 400 to about 650nanometers, that is in the visible region of the light spectrum. Inembodiments thereof, the imaging members of the present inventiongenerally possess broad spectral response to white light or,specifically to red, green and blue light emitting diodes and stableelectrical properties over long cycling times. Many of the unsymmetricalperylene bisimide dimers of the present invention when selected asphotogenerator pigments, exhibit excellent charge acceptance of about800 volts surface potential in a layered device, dark decay of less thanabout 50 volts per second, for example 35 to 45, photosensitivitiesranging from E_(1/2) of about 4 to about 20 ergs/centimeter, excellentdispersibility and low solubility in typical coating compositions, suchas solutions of certain polymers in organic solvents, such as methylenechloride, selected for the preparation of layered photoresponsiveimaging members.

PRIOR ART

Generally, layered photoresponsive imaging members are described in anumber of U.S. patents, such as U.S. Pat. No. 4,265,900, the disclosureof which is totally incorporated herein by reference, wherein there isillustrated an imaging member comprised of a photogenerating layer, andan aryl amine hole transport layer. Examples of photogenerating layercomponents include trigonal selenium, metal phthalocyanines, vanadylphthalocyanines, and metal free phthalocyanines. Additionally, there isdescribed in U.S. Pat. No. 3,121,006 a composite xerographicphotoconductive member comprised of finely divided particles of aphotoconductive inorganic compound dispersed in an electricallyinsulating organic resin binder. The binder materials disclosed in the'006 patent comprise a material which is substantially incapable oftransporting for any significant distance injected charge carriersgenerated by the photoconductive particles.

The selection of selected perylene pigments as photoconductivesubstances is also known. There is thus described in Hoechst EuropeanPatent Publication 0040402, DE3019326, filed May 21, 1980, the use ofN,N'-disubstituted perylene-3,4,9,10-tetracarboxyldiimide pigments asphotoconductive substances. Specifically, there is, for example,disclosed in this publicationN,N'-bis(3-methoxypropyl)perylene-3,4,9,10-tetracarboxyldiimide duallayered negatively charged photoreceptors with improved spectralresponse in the wavelength region of 400 to 700 nanometers. A similardisclosure is presented in Ernst Gunther Schlosser, Journal of AppliedPhotographic Engineering, Vol. 4, No. 3, page 118 (1978). There are alsodisclosed in U.S. Pat. No. 3,871,882 photoconductive substancescomprised of specific perylene-3,4,9,10-tetracarboxylic acid derivativedyestuffs. In accordance with the teachings of this patent, thephotoconductive layer is preferably formed by vapor depositing thedyestuff in a vacuum. Also, there is specifically disclosed in thispatent dual layer photoreceptors with perylene-3,4,9,10-tetracarboxylicacid diimide derivatives, which have spectral response in the wavelengthregion of from 400 to 600 nanometers. Further, in U.S. Pat. No.4,555,463, the disclosure of which is totally incorporated herein byreference, there is illustrated a layered imaging member with achloroindium phthalocyanine photogenerating layer. In U.S. Pat. No.4,587,189, the disclosure of which is totally incorporated herein byreference, there is illustrated a layered imaging member with anonhalogenated perylene pigment photogenerating component. Both of theaforementioned patents disclose an aryl amine component as a holetransport. layer.

Moreover, there are disclosed in U.S. Pat. No. 4,419,427 electrographicrecording media with a photosemiconductive double layer comprised of afirst layer containing charge carrier perylene diimide dyes, and asecond layer with one or more compounds which are charge transportingmaterials when exposed to light, reference the disclosure in column 2,beginning at line 20. The two general types of monomeric perylenepigment, illustrated as follows in Formula 3, are commonly referred toas perylene bis(imides) and bis(imidazo) perylenes.

FORMULA 3 Perylene Bisimide (3a) and Bisimidazo (3b) Pigments ##STR4##wherein R=alkyl, aryl, aralkyl, etc.; Ar=1,2-phenylene, 18-naphthalene,and the like.

These perylenes can be prepared by reacting perylene tetracarboxylicacid dianhydride with primary amines or with diamino-aryl or alkylcompounds. Their use as photoconductors is disclosed in U.S. Pat. Nos.3,871,882, the disclosure of which is totally incorporated herein byreference, and 3,904,407. The '882 patent discloses the use of theperylene dianhydride and bisimides in general (Formula 3a, R═H, loweralkyl (C1 to C4), aryl, substituted aryl, aralkyl, a heterocyclic groupor the NHR' group in which R' is phenyl, substituted phenyl or benzoyl)as vacuum evaporated thin charge generation layers (CGLs) inphotoconductive devices coated with a charge transporting layer (CTL).The '407 patent, the disclosure of which is totally incorporated hereinby reference, illustrates the use of bisimide compounds (Formula 3a,R=alkyl, aryl, alkylaryl, alkoxyl or halogen, or heterocyclicsubstituent) with preferred pigments being R=chlorophenyl ormethoxyphenyl. This patent illustrates the use of certain vacuumevaporated perylene pigments or a highly loaded dispersion of pigment ina binder resin as charge generating layer (CGL) in layeredphotoreceptors with a CTL overcoat or, alternatively, as a single layerdevice in which the perylene pigment is dispersed in a chargetransporting active polymer matrix. The use of purple to violetdyestuffs with specified chromaticity values, including bisimidazoperylenes, specifically cis and trans bis(benzimidazo)perylene (Formula3b, X=1,2-phenylene) and bis(1,8-naphthimidazo)perylene (Formula 3b,X=1,8-naphthylene), is disclosed in U.S. Pat. No. 3,972,717. This patentalso describes the use of vacuum-evaporated CGLs in layeredphotoconductive devices. The use of a plurality of pigments, inclusiveof perylenes, in vacuum evaporated CGLs is illustrated in U.S. Pat. No.3,992,205.

U.S. Pat. No. 4,419,427 discloses the use of highly-loaded dispersionsof perylene bisimides, with bis(2,6-dichlorophenylimide) being apreferred material, in binder resins as CGL layers in devices overcoatedwith a charge transporting layer such as a poly(vinylcarbazole)composition. U.S. Pat. No. 4,429,029 illustrates the use, in devicessimilar to those of the '427 patent, of bisimides and bisimidazoperylenes in which the perylene nucleus is halogenated, preferably to anextent where 45 to 75 percent of the perylene ring hydrogens have beenreplaced by halogen. U.S. Pat. No. 4,587,189, the disclosure of which istotally incorporated herein by reference, illustrates layeredphotoresponsive imaging members prepared with highly-loaded dispersionsor, preferably, vacuum evaporated thin coatings of cis- andtrans-bis(benzimidazo)perylene (3a, X=1,2-phenylene) and other perylenesovercoated with hole transporting compositions comprised of a variety ofN,N,N',N'-tetraaryl-4,4'-diaminobiphenyls. U.S. Pat. No. 4,937,164illustrates the use of perylene bisimides and bisimidazo pigments inwhich the 1,12-and/or 6,7 position of the perylene nucleus is bridged byone or two sulfur atoms wherein the pigments in the CGL layers areeither vacuum evaporated or dispersed in binder resins and a layer oftetraaryl biphenyl hole transporting molecules.

U.S. Pat. No. 4,517,270 illustrates bisimides with propyl,hydroxypropyl, methoxypropyl and phenethyl substituents (3a, R=CH₃ CH₂CH₂ --, HOCH₂ CH₂ CH₂ --, CH₃ OCH₂ CH₂ CH₂ --, and C₆ H₅ CH₂ CH₂ --)which are black or dark primarily because of their crystal properties,and perylene pigments which are nuclearly substituted with anilino,phenylthio, or p-phenylazoanilino groups. Pigments of this type wereindicated as providing good electrophotographic recording media withpanchromatic absorption characteristics. Similarly, in U.S. Pat. No.4,719,163 and U.S. Pat. No. 4,746,741 the pigmentN,N'-bis(2-(3-methylphenyl)ethyl)perylene-3,4,9,10-bis(dicarboximide)(3a, R=3-methyl-C₆ H₅ CH₂ CH₂ --) is indicated as providing layeredelectrophotographic devices having spectral response to beyond 675nanometers.

Two additional patents relating to the use of perylene pigments inlayered photoreceptors are U.S. Pat. No. 5,019,473, which illustrates agrinding process to provide finely and uniformly dispersed perylenepigment in a polymeric binder with excellent photographic speed, andU.S. Pat. No. 5,225,307, the disclosure of which is totally incorporatedherein by reference, which discloses a vacuum sublimation process whichprovides a photoreceptor pigment, such as bis(benzimidazo)perylene (3b,X=1,2-phenylene) with superior electrophotographic performance.

The following patents relate to the use of perylene compounds, either asdissolved dyes or as dispersions in single layer electrophotographicphotoreceptors usually based on sensitized poly(vinyl carbazole)compositions: U.S. Pat. Nos. 4,469,769; 4,514,482; 4,556,622; JapaneseJP 84-31,957, -119,356, -119,357, -140,454, -140,456, -157,646,-157,646, and -157,651.

While the above described layered perylene-based photoreceptors, orphotoconductive imaging members may exhibit desirable xerographicelectrical characteristics, most of the bisimides are red to brown incolor, and possess, it is believed, relatively poor spectral response,particularly to the 600 to 700 nanometers region of the spectrum. Themajority of the bis(imidazo) pigments, especially those with a purple toviolet color, have poor spectral response in the blue (400 to 450nanometers) region of the spectrum. Ideally, a photoconductive pigmentused for light lens imaging, particularly for color photocopying, shouldhave a uniform spectral response, that is, be panchromatic throughoutthe visible spectrum from about 400 to about 700 nanometers.

Although a number of known imaging members are suitable for theirintended purposes, a need remains for imaging members containingimproved photogenerator pigments. In addition, a need exists for imagingmembers containing photoconductive components with improved xerographicelectrical performance including higher charge acceptance, lower darkdecay, increased charge generation efficiency and charge injection intothe transporting layer, tailored PIDC curve shapes to enable a varietyof reprographic applications, reduced residual charge and/or reducederase energy, improved long term cycling performance, and lessvariability in performance with environmental changes in temperature andrelative humidity. There is also a need for imaging members withphotoconductive components comprised of certain photogenerating pigmentswith enhanced dispersability in polymers and solvents. There is also aneed for photogenerating pigments which permit the preparation ofcoating dispersions, particularly in dip-coating operations, which arecolloidally stable and wherein settlement is avoided or minimized, forexample little settling for a period of from 20 to 30 days in theabsence of stirring. Further, there is a need for photoconductivematerials with enhanced dispersability in polymers and solvents thatenable low cost coating processes in the manufacture of photoconductiveimaging members. Additionally, there is a need for photoconductivematerials that enable imaging members with enhanced photosensitivity inthe red region of the light spectrum, enabling the resulting imagingmembers thereof to be selected for imaging by red diode and gas lasers.Furthermore, there is a need for photogenerator pigments with spectralresponse in the green and blue regions of the spectrum to enable imagingby newly emerging blue and green electronic imaging light sources. Aneed also exists for improved panchromatic pigments with broad spectralresponse from about 400 to 700 nanometers for color copying usinglight-lens processes. There also is a need for photogenerating pigmentswhich can be readily prepared from commercially available reactants, andfor preparative processes and purification techniques which providehighly pure pigment with outstanding xerographic electrical performance,without recourse to expensive and time consuming post-syntheticpurification methods such as solvent extraction or vacuum sublimation.These and other needs may be accomplished, it is believed, inembodiments of the present invention.

SUMMARY OF THE INVENTION

Examples of objects of the present invention include:

It is an object of the present invention to provide unsymmetricalperylene bisimide dimers and imaging members thereof with many of theadvantages illustrated herein.

It is another object of the present invention to provide imaging memberswith novel photoconductive components with improved photoconductivity.

Additionally in another object of the present invention there areprovided (1) unsymmetrical perylene bisimide dimers suitable for use asdispersed colorants in polymeric composites and as photogeneratorpigments in layered photoconductive imaging devices; (2) unsymmetricalperylene bisimide dimers comprised of two perylene bisimide moietiesjoined together by an unsymmetrical bridging group; processes for thepreparation of dimeric pigments from readily available startingmaterials; and processes for the purification of these dimers whichenable photoelectrically stable materials for their selection asphotogenerator pigments in photoconductive imaging devices, or members;and wherein two perylene moieties are linked together by imidenitrogens.

It is another object of the present invention to provide photoconductiveimaging members with unsymmetrical perylene dimer photogeneratingpigments with the formulas illustrated herein, and that enable imagingmembers with improved photosensitivity in the visible wavelength regionof light spectrum, such as from about 400 to about 700 nanometers.

It is another object of the present invention to provide unsymmetricaldimeric pigments which can possess a variety of colors such as magenta,red, brown, black, green, and the like; the color being primarilydependent on the types of terminal and bridging groups present.

Still, another object of the present invention relates to the provisionof novel compounds, and more specifically, compounds of the formulasillustrated herein.

Another object of the present invention relates to the preparation ofunsymmetrical perylene dimer photogenerating pigments having structuresillustrated in Formula 1.

Embodiments of the present invention relate to the provision of layeredimaging members comprised of a supporting substrate, a photogeneratinglayer comprised of photogenerating pigments comprised of unsymmetricalperylene bisimide dimers, such as those of Formula 1, and morespecifically, wherein R is hydrogen, alkyl, such as methyl, ethyl,n-propyl, n-butyl, isobutyl, n-pentyl, 2-methylbutyl, 3-methylbutyl,n-hexyl, phenyl, benzyl, phenethyl and the like, and X-Y is anunsymmetrical bridging group such as alkylene, arylene, aralkylene, andthe like.

Unsymmetrical alkylenes, representative formulas of which areillustrated hereinafter, include 1,2-propylene, 1-methyl-1,3-propylene,1-ethyl-1,3-propylene, 1-methyl-1,4-tetramethylene,2-methyl-1,4-tetramethylene, 1-methyl-1,5-pentamethylene,2-methyl-1,5-pentamethylene and higher unsymmetric alkylene groups withup to about 20 carbon atoms. Unsymmetric substituted alkylenes include,for example, 3-hydroxy-1,2-propylene, 2-hydroxy-1,4-tetramethylene,2-methoxy-1,4-tetramethylene, 2-carboxy-1,4-tetramethylene and2-dimethylamino-1,4-tetramethylene. Arylene refers, for example, tounsymmetrically substituted bridging groups such as 2,4-, 2,3'-, 2,4'-,and 3,4'-biphenylene, and 1,3-, 1,6- and 1,7-naphthylene. Substitutedarylenes refers, for example, to groups such as 2-chloro-1,4-phenylene,2-methyl-4,4'-biphenylene, N-phenylbenzamide-3,4'-diyl,diphenylsulfone-3,4'-diyl and diphenylether-3,4'-diyl. Aralkyleneincludes benzyl-, phenethyl-, phenylpropyl- and fluorenyl-groups inwhich one perylene bisimide moiety is bonded to the alkyl group and thesecond is bonded to the 2-, 3- or 4-position of the aromatic ring.Substituted aralkylene refers, for example, to groups of theaforementioned class in which substituents such as methyl,tertiary-butyl, halogen of, for example, fluoro, chloro, bromo, andiodo, hydroxy, methoxy, nitro, cyano and dimethylamino are attached tothe aromatic ring.

In embodiments, the imaging members of the present invention arecomprised of, preferably in the order indicated, a conductive substrate,a photogenerating layer comprising unsymmetrical perylene bisimide dimerpigments dispersed in a resinous binder composition, and a chargetransport layer, which comprises charge transporting molecules dispersedin an inactive resinous binder composition.

In embodiments, the photoconductive imaging member comprises aconductive substrate, a hole transport layer comprising a hole transportcomposition, such as an aryl amine, dispersed in an inactive resinousbinder composition, and as a top layer a photogenerating layer comprisedof unsymmetrical perylene bisimide dimer pigments optionally dispersedin a resinous binder composition; or a conductive substrate, a holeblocking metal oxide layer, an optional adhesive layer, aphotogenerating layer comprised of the unsymmetrical perylene bisimidedimer pigment of the present invention, optionally dispersed in aresinous binder composition, and an aryl amine hole transport layercomprising aryl amine hole transport molecules optionally dispersed in aresinous binder.

Specific examples of unsymmetrical perylene dimer pigments of thepresent invention and encompassed by the Formula 1 illustrated hereininclude those wherein R is hydrogen, methyl, ethyl, n-propyl, isopropyl,3-methoxypropyl, 3-hydroxypropyl, cyclopropyl, cyclopropylmethyl,n-butyl, isobutyl, secbutyl, cyclobutyl, n-pentyl, 2-pentyl, 3-pentyl,2-(3-methyl)butyl, 2-methylbutyl, 3-methylbutyl, neopentyl, cyclopentyl,n-hexyl, 2-ethylhexyl, cyclohexyl, n-heptyl, cycloheptyl, n-octyl,cyclooctyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, cyclododecyl,phenyl, benzyl, phenethyl and substituted phenyl, benzyl and phenethylradicals in which the aromatic ring contains from 1 to 5 substituentsinclusive of fluorine, chlorine, bromine, iodine, methyl, hydroxymethyl,trifluoromethyl, tertiary-butyl, tertiary-butoxy, methoxy,trifluoromethoxy, nitro, cyano, dimethylamino, diethylamino, and thelike and X-Y represents an unsymmetrical bridging group inclusive of,but not limited to, the following specific examples. ##STR5##

Examples of Unsymmetrical X-Y Bridging Groups ##STR6##

Specific examples of photogenerating unsymmetric perylene bisimidedimers of the present invention include those encompassed by Formula 1wherein R is hydrogen, methyl, ethyl, n-propyl, allyl, 3-methoxypropyl,n-butyl, isobutyl, n-pentyl, 2-methylbutyl, 3-methylbutyl, neopentyl,n-hexyl, n-heptyl, n-octyl, phenyl, benzyl, 3-chlorobenzyl andphenethyl, and X-Y is propane-1,2-diyl, butane-1,2-diyl,butane-1,3-diyl, 2-methylbutane-1,4-diyl, pentane-1,3-diyl,pentane-1,4-diyl, 2-methylpentane-1,5-diyl, toluene-a,4-diyl,ethylbenzene-b,4-diyl and diphenyl ether-3',4'-diyl.

The substrate can be formulated entirely of an electrically conductivematerial, or it can be comprised of an insulating material having anelectrically conductive surface. The substrate can be of an effectivethickness, generally up to about 100 mils, and preferably from about 1to about 50 mils, although the thickness can be outside of this range.The thickness of the substrate layer depends on many factors, includingeconomic and mechanical considerations. Thus, this layer may be ofsubstantial thickness, for example over 100 mils, or of minimalthickness provided that there are no adverse effects thereof. In aparticularly preferred embodiment, the thickness of this layer is fromabout 3 mils to about 10 mils. The substrate can be opaque orsubstantially transparent and can comprise numerous suitable materialshaving the desired mechanical properties. The entire substrate cancomprise the same material as that in the electrically conductivesurface, or the electrically conductive surface can merely be a coatingon the substrate. Any suitable electrically conductive material can beemployed. Typical electrically conductive materials include copper,brass, nickel, zinc, chromium, stainless steel, conductive plastics andrubbers, aluminum, semitransparent aluminum, steel, cadmium, titanium,silver, gold, paper rendered conductive by the inclusion of a suitablematerial therein or through conditioning in a humid atmosphere to ensurethe presence of sufficient water content to render the materialconductive, indium, tin, metal oxides, including tin oxide and indiumtin oxide, and the like. The substrate layer can vary in thickness oversubstantially wide ranges depending on the desired use of theelectrophotoconductive member. Generally, the conductive layer ranges inthickness of from about 50 ÅAngstroms to many centimeters, although thethickness can be outside of this range. When a flexibleelectrophotographic imaging member is desired, the thickness typicallyis from about 100 ÅAngstroms to about 750 ÅAngstroms. The substrate canbe of any other conventional material, including organic and inorganicmaterials. Typical substrate materials include insulating nonconductingmaterials such as various resins known for this purpose includingpolycarbonates, polyamides, polyurethanes, paper, glass, plastic,polyesters such as MYLAR® (available from E. I. DuPont) or MELINEX 447®(available from ICI Americas, Inc.), and the like. If desired, aconductive substrate can be coated onto an insulating material. Inaddition, the substrate can comprise a metallized plastic, such astitanized or aluminized MYLAR®, wherein the metallized surface is incontact with the photogenerating layer or any other layer situatedbetween the substrate and the photogenerating layer. The coated oruncoated substrate can be flexible or rigid, and can have any number ofconfigurations, such as a plate, a cylindrical drum, a scroll, anendless flexible belt, or the like. The outer surface of the substratepreferably comprises a metal oxide such as aluminum oxide, nickel oxide,titanium oxide, and the like.

In embodiments, intermediate adhesive layers between the substrate andsubsequently applied layers may be desirable to improve adhesion. Whensuch adhesive layers are utilized, they preferably have a dry thicknessof from about 0.1 micron to about 5 microns, although the thickness canbe outside of this range. Typical adhesive layers include film-formingpolymers such as polyester, polyvinylbutyral, polyvinylpyrrolidone,polycarbonate, polyurethane, polymethylmethacrylate, and the like aswell as mixtures thereof. Since the surface of the substrate can be ametal oxide layer or an adhesive layer, the expression substrate isintended to also include a metal oxide layer with or without an adhesivelayer on a metal oxide layer. Moreover other known layers may beselected for the photoconductive imaging members of the presentinvention, such as polymer protective overcoats, and the like.

The photogenerating layer is of an effective thickness, for example, offrom about 0.05 micron to about 10 microns or more, and in embodimentshas a thickness of from about 0.1 micron to about 3 microns. Thethickness of this layer can be dependent primarily upon theconcentration of photogenerating material in the layer, which maygenerally vary from about 5 to 100 percent. The 100 percent valuegenerally occurs when the photogenerating layer is prepared by vacuumevaporation of the pigment. When the photogenerating material is presentin a binder material, the binder contains, for example, from about 25 toabout 95 percent by weight of the photogenerating material, andpreferably contains about 60 to 80 percent by weight of thephotogenerating material. Generally, it is desirable to provide thislayer in a thickness sufficient to absorb about 90 to about 95 percentor more of the incident radiation which is directed upon it in theimagewise or printing exposure step. The maximum thickness of this layeris dependent primarily upon factors such as mechanical considerations,such as the specific photogenerating compound selected, the thicknessesof the other layers, and whether a flexible photoconductive imagingmember is desired.

Typical transport layers are described, for example, in U.S. Pat. Nos.,4,265,990; 4,609,605; 4,297,424 and 4,921,773, the disclosures of eachof these patents being totally incorporated herein by reference. Organiccharge transport materials can also be employed.

Hole transport molecules of the type described in U.S. Pat. Nos.4,306,008; 4,304,829; 4,233,384; 4,115,116; 4,299,897; 4,081,274, and5,139,910, the disclosures of each are totally incorporated herein byreference, can be selected for the imaging members of the presentinvention. Typical diamine hole transport molecules includeN,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine,N,N'-diphenyl-N,N'-bis(4-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine,N,N'-diphenyl-N,N'-bis(2-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine,N,N'-diphenyl-N,N'-bis(3-ethylphenyl)-(1,1'-biphenyl)-4,4'-diamine,N,N'-diphenyl-N,N'-bis(4-ethylphenyl)-(1,1'-biphenyl)-4,4'-diamine,N,N'-diphenyl-N,N'-bis(4-n-butylphenyl)-(1,1'-biphenyl)-4,4'-diamine,N,N'-diphenyl-N,N'-bis(3-chlorophenyl)-(1,1'-biphenyl)-4,4'-diamine,N,N'-diphenyl-N,N'-bis(4-chlorophenyl)-(1,1'-biphenyl)-4,4'-diamine,N,N'-diphenyl-N,N'-bis(phenylmethyl)-(1,1'-biphenyl)-4,4'-diamine,N,N,N',N'-tetraphenyl- 2,2'-dimethyl-1,1'-biphenyl!-4,4'-diamine,N,N,N',N'-tetra-(4-methylphenyl)-2,2'-dimethyl-1,1'-biphenyl!-4,4'-diamine,N,N'-diphenyl-N,N'-bis(4-methylphenyl)-2,2'-dimethyl-1,1'-biphenyl!-4,4'-diamine,N,N'-diphenyl-N,N'-bis(2-methylphenyl)-2,2'-dimethyl-1,1'-biphenyl!-4,4'-diamine,N,N'-diphenyl-N,N'-bis(3-methylphenyl)-2,2'-dimethyl-1,1'-biphenyl!-4,4'-diamine,N,N'-diphenyl-N,N'-bis(3-methylphenyl)-pyrenyl-1,6-diamine, and thelike.

In embodiments of the present invention, the preferred hole transportlayer, since it enables excellent effective transport of charges, iscomprised of aryldiamine components as represented, or essentiallyrepresented, by the general formula of, for example, the U.S. patentsindicated herein, such as 4,265,990, wherein X, Y and Z are selectedfrom the group consisting of hydrogen, an alkyl group with, for example,from 1 to about 25 carbon atoms and a halogen, preferably chlorine, andat least one of X, Y and Z is independently an alkyl group or chlorine.When Y and Z are hydrogen, the compound may beN,N'-diphenyl-N,N'-bis(alkylphenyl)-(1,1'-biphenyl)-4,4'-diamine whereinalkyl is, for example, methyl, ethyl, propyl, n-butyl, or the like, orthe compound may beN,N'-diphenyl-N,N'-bis(chlorophenyl)-(1,1'-biphenyl)-4,4'-diamine.

The charge transport component is present in the charge transport layerin an effective amount, generally from about 5 to about 90 percent byweight, preferably from about 20 to about 75 percent by weight, and morepreferably from about 30 to about 60 percent by weight, although theamount can be outside of this range.

Examples of the highly insulating and transparent resinous components orinactive binder resinous material for the transport layer includebinders such as those described in U.S. Pat. No. 3,121,006, thedisclosure of which is totally incorporated herein by reference.Specific examples of suitable organic resinous materials includepolycarbonates, acrylate polymers, vinyl polymers, cellulose polymers,polyesters, polysiloxanes, polyamides, polyurethanes, polystyrenes, andepoxies as well as block, random or alternating copolymers thereof.Preferred electrically inactive binder materials are polycarbonateresins having a molecular weight of from about 20,000 to about 100,000with a molecular weight in the range of from about 50,000 to about100,000 being particularly preferred. Generally, the resinous bindercontains from about 5 to about 90 percent by weight of the activematerial corresponding to the foregoing formula, and preferably fromabout 20 percent to about 75 percent of this material.

Similar binder materials may be selected for the photogenerating layer,including polyesters, polyvinyl butyrals, polyvinylcarbazole,polycarbonates, polyvinyl formals, poly(vinylacetals) and thoseillustrated in U.S. Pat. No. 3,121,006, the disclosure of which istotally incorporated herein by reference.

The photoconductive imaging member may optionally contain a chargeblocking layer situated between the conductive substrate and thephotogenerating layer. This layer may comprise metal oxides, such asaluminum oxide and the like, or materials such as silanes and nylons.Additional examples of suitable materials include polyisobutylmethacrylate, copolymers of styrene and acrylates such asstyrene/n-butyl methacrylate, copolymers of styrene and vinyl toluene,polycarbonates, alkyl substituted polystyrenes, styrene-olefincopolymers, polyesters, polyurethanes, polyterpenes, siliconeelastomers, mixtures thereof, copolymers thereof, and the like. Theprimary purpose of this layer is to prevent charge injection from thesubstrate during and after charging. This layer is of a thickness ofless than 50 ÅAngstroms to about 10 microns, preferably being no morethan about 2 microns.

In addition, the photoconductive imaging member may also optionallycontain an adhesive interface layer situated between the hole blockinglayer and the photogenerating layer. This layer may comprise a polymericmaterial such as polyester, polyvinyl butyral, polyvinyl pyrrolidone andthe like. Typically, this layer is of a thickness of less than about 0.6micron.

The unsymmetrical dimers of the present invention can be readilyprepared by reaction, or condensation of about 2 to about 5 equivalentsof a perylene monoimide-monoanhydride as illustrated in Formula 2, withone equivalent of an unsymmetrical diamine such as 1,2-diaminopropane,2-methyl-1,5-diaminopentane, 4-aminobenzylamine, 4-aminophenethylamine,3,4'-diaminodiphenyl ether, 4,4'-diaminobenzanilide or3,4'-diaminodiphenylsulfone in an organic solvent, such aschloronaphthalene, trichlorobenzene, decalin, tetrafin, aniline,dimethylformamide, dimethylsulfoxide, N-methylpyrrolidone and the likewith the optional use of appropriate catalysts, such as zinc acetate orzinc iodide, in an amount equivalent to about 1 to 50 mole percent ofthe perylene. The concentration of reactants in the solvent can rangefrom about 50 weight percent combined diamine and anhydride, and 50percent solvent to about 2 percent diamine and anhydride, and 98 percentsolvent with a preferred range being from about 5 percent diamine andarthydride and 95 percent solvent to 20 percent dinmine and arthydrideand 80 percent solvent. The reactants are stirred in the solvent andheated to a temperature of from about 100° C. to 300° C., and preferablyfrom 150° C. to 205° C. for a period of from 10 minutes to about 8 hoursdepending on the rate of the reaction. The mixture is subsequentlycooled to a temperature of between about 25° C. to about 175° C., andthe solid pigment perylene product is separated from the mother liquorsby filtration through, for example, a fine porosity sintered glassfilter funnel or a glass fiber filter. The pigment product is thensubjected to a number of washing steps using hot and cold solvents suchas dimethyl formamide, methanol, water and alcohols. Optionally, thepigment may be washed with dilute hot or cold aqueous base solution suchas 5 percent of sodium hydroxide or potassium carbonate which serves toremove by conversion to a water soluble salt any residual startinganhydride and other acidic contaminants. Also, optionally theunsymmetrical dimeric perylene pigment product may also be washed withdilute acid such as 2 percent aqueous hydrochloric acid which serves toremove residual metal salts, such as for example zinc acetate which canbe optionally used as a reaction catalyst. Finally, the pigment is driedeither at ambient temperature or at temperatures up to 200° C. atatmospheric pressure or under vacuum. The yield of product, referred toas "as-synthesized pigment", ranges from about 50 percent to nearly 100percent.

More specifically, the process of the present invention comprisesstirring a mixture of 2.2 molar equivalents of a perylenetetracarboxylic acid mono imide-mono anhydride having the structure ofFormula 2 with R=n-propyl, n-phenyl and the like inN-methylpyrrolidinone solvent in an amount corresponding to about 50parts by weight of solvent to about 2 parts of monoanhydride at roomtemperature, followed by adding 1 molar equivalent of an unsymmetricdiamine, such as 2-methyl-1,5-diaminopentane or 4-aminobenzylamine and,optionally, a catalyst known to speed up the reaction of amine withanhydrides, such as zinc acetate dihydrate, in an amount correspondingto about 0.5 equivalents, to this mixture. Stirring this mixture andheating until the solvent begins to reflux (N-methylpyrrolodinone boilsat 202° C.) during which treatment the diamine reacts sequentially withtwo molecules of the monoanhydride to form the dimeric perylene pigmentmolecule. Maintaining the heating and stirring at the solvent refluxtemperature for a period of about 2 hours ensures completion of thereaction. Thereafter, cooling the reaction mixture to about 150° C. andfiltering the mixture through a filter such as fine-porosity sinteredglass of a glass-fiber filter which has been preheated to about 150° C.with, for example, boiling solvent such as dimethylformamide (DMF).Washing the pigment in the filter with DMF heated to about 150° C.(which serves to dissolve and thus remove any residual startinganhydride) until the color of the filtrate wash becomes, and remains,colorless or light orange was then accomplished. The pigment is thenwashed with DMF at room temperature, about 25° C., and is finally washedwith acetone, methanol or a similar low-boiling solvent and is dried at60° C. in an oven.

Optionally, water can be used in the final washing step and the pigmentwet cake can be freeze dried. This process generally providesfree-flowing pigment which is more readily redispersed in solvent thansolvent washed pigment which has been dried using other methods whichcan sometimes result in the formation of a hard, caked mass of pigmentwhich is difficult to redisperse.

Also optionally, in situations where the hot, for example 60° to 150°C., solvent, for example DMF, fails to completely remove all the excessstarting monoanhydride from the dimer the product can be dispersed indilute, for example 1 to 5 percent of aqueous potassium hydroxide for aperiod of time of from about 1 hour to about 24 hours, and preferablyfrom about 7 to about 20 hours, at room temperature, about 25° C. toabout 90° C., which treatment converts the monoimide to a water-soluble,deep purple-colored dipotassium carboxylate salt, followed by filtrationand washing the solid with water until the filtrate becomes colorless.The residual starting anhydride in the product can be detected by knownspectroscopic methods such as FT-IR and NMR, or by a color spot test inwhich the product is stirred in dilute, for example about 2 percent ofaqueous potassium hydroxide solution with the presence of monoanhydridebeing indicated by the development of a deep reddish purple colorcharacteristic of the dipotassium salt of the monoimide.

Also optionally, in situations where a metal-containing catalyst, suchas zinc acetate dihydrate, has been used to improve the reaction ratethe product can be stirred in a dilute acid, such as 2 percent aqueoushydrochloric acid, which process coverts the residual metal to watersoluble salts, which can then be removed by filtration and washing withwater.

The unsymmetrical photogenerating compounds of the present invention inembodiments thereof enable enhanced photosensitivity in the visiblewavelength range. In particular, imaging members with photosensitivityat wavelengths of from about 400 to 700 nanometers are provided inembodiments of the present invention, which renders them particularlyuseful for color copying and imaging and printing applications, such asred LED and diode laser printing processes, which typically requiresensitivity from about 600 to about 700 nanometers.

The present invention also encompasses a method of generating imageswith the photoconductive imaging members disclosed herein. The methodcomprises the steps of generating an electrostatic latent image on aphotoconductive imaging member of the present invention, developing thelatent image with a toner comprised of resin, pigment like carbon black,and a charge additive, and transferring the developed electrostaticimage to a substrate. Optionally, the transferred image can bepermanently affixed to the substrate. Development of the image may beachieved by a number of methods, such as cascade, touchdown, powdercloud, magnetic brush, and the like. Transfer of the developed image toa substrate, such as paper, may be by any method, including those makinguse of a corotron or a biased roll. The fixing step may be performed bymeans of any suitable method, such as flash fusing, heat fusing,pressure fusing, vapor fusing, and the like. Any substrate selected forxerographic copiers and printers, including digital copiers, may be usedas a substrate, such as paper, transparency material, and the like.

Specific embodiments of the invention will now be described in detail.These Examples are intended to be illustrative, and the invention is notlimited to the materials, conditions, or process parameters set forth inthese embodiments. All parts and percentages are by weight unlessotherwise indicated.

SYNTHESIS EXAMPLES

The starting monoanhydride monoimides in the following Examples wereprepared by the methods described in U.S. Pat. No. 4,501,906, thedisclosure of which is totally incorporated herein by reference,(Hoechst) or by minor adaptations of the processes described therein.The structures of the product dimers described below were mainlyestablished by ¹ H and ¹³ C nuclear magnetic resonance spectrometry intrifluoroacetic acid-containing solvent mixtures. Visible absorptionspectra in trifiuoroacetic acid-methylene chloride solution were alsomeasured for each product. The bisimide dimers evidence absorbancemaxima at about 500 and 540 nanometers which is diagnostic for theperylene bisimide chromophore in this solvent system. Trivial names,based on the substituent groups and referring to the perylene bisimidemoiety as the imidoperyleneimido group have been used. To avoid orminimize confusion and ambiguity, the compounds are also described inrelation to the structures shown in Formula 1.

The synthesis Examples that follow are representative of the generalsynthesis and purification processes selected.

SYNTHESIS EXAMPLE 1 Preparation of1,5-Bis(n-butylimidoperyleneimido)-2-methylpentane (Formula 1, R andR=n-butyl, X-Y=2-methyl-1,5-pentamethylene)

A suspension of mono-n-butylimidoperylene monoanhydride (Formula 2,R=n-butyl; 2.46 grams, 0.0055 mole) in 100 milliliters ofN-methylpyrollidinone (NMP) was treated with 0.2905 gram (0.338milliliter, 0.00250 mole) of 1,5-diamino-2-methylpentane (Dytek A). Theresulting mixture was then stirred and was heated to reflux (202° C.)for 21/2 hours. The resultant thick dark brown reaction mixture wascooled to 150° C. then was filtered through a 9 centimeter glass fiberfilter, Whatman Grade 934AH, which had been preheated by pouring 100milliliters of boiling dimethylformamide (DMF) solvent (boiling point150° C.) through it. The resulting solid product was washed in thefunnel with 3×75 milliliters portions of boiling DMF. The final washfiltrate was a faint pink color. The solid was washed with 25milliliters of cold DMF then with 2×25 milliliters of methanol and wasdried at 60° C. to provide 2.25 grams (92 percent yield) of darkchocolate brown solid product.

A spot test for the presence of starting monoanhydride which wasaccomplished by stirring about 50 milligrams of the above productpigment in 2 milliliters of 2 percent aqueous potassium hydroxidesolution for 4 hours at room temperature, about 25° C., was negative,there being no sign of the deep red-purple color characteristic of themonoimide dicarboxylate salt.

SYNTHESIS EXAMPLE 2 Preparation of1,5-Bis(n-pentylimidoperyleneimido)-2-methylpentane (Formula 1, R andR=n-pentyl, X-Y=2-methyl-1,5-pentamethylene)

A mixture of 2.54 grams (0.0055 mole) of mono-n-pentylimidoperylenemonoanhydride (Formula 2, R=n-pentyl) and Dytek A diamine (0.338milliliter, 0.00250 mole/in 100 milliliters of NMP was stirred andheated at reflux (202° C.) for 2.74 hours, then was cooled to 150° C.The solid product resulting was hot filtered and washed with boilingDMF, cold DMF and methanol as in the above Example 1. Drying at 60° C.for 16 hours provided 2.20 grams (88 percent yield) of a brownish redsolid product. A spot test for the presence of starting monoimide wasnegative.

SYNTHESIS EXAMPLE 3 Preparation ofBis-1,3-(n-propylimidoperyleneimido)-1-ethylpropane (Formula 1, R andR=n-propyl, X-Y=1-ethyl-1,3-propylene)

A suspension of 4.76 grams (0.011 mole) of monopropylimidoperylenemonoanhydride (Formula 2, R=n-propyl) in 300 milliliters of NMP wastreated with 0.511 gram (0.598 milliliters, 0.005 mole) of1,3-diaminopentane (Dytek EP). The resulting mixture was stirred at roomtemperature, about 25° C. throughout, for 15 minutes, then was heated atreflux for 21/2 hours. The resultant dark reddish brown solution wascooled to room temperature and was filtered. The solid product waswashed with DMF until the filtrate became a light orange color. Thesolid was washed with 2×20 milliliters of methanol and then was dried at60° C. to provide 2.6 grams of a brown solid product ofbis-1,3-(n-propylimidoperyleneimido)-1-ethylpropane (Formula 1,R=n-propyl, X-Y=1-ethyl-1,3-propylene).

When a sample, about 10 grams, of the above obtained product was stirredin a 2 percent aqueous solution of potassium hydroxide, a reddish purplecolor developed which is indicative of residual starting anhydride inthe product. The product was stirred in 200 milliliters of watercontaining 4 grams of potassium hydroxide for 5 hours at about 60° C.,the resultant suspension was filtered, and the solid product was washedwith 5×100 milliliters of water until the filtrate changed from reddishpurple to colorless. The solid was then dried at 60° C. to provide 1.3gram (28 percent yield) of the above dark brown solid product.

SYNTHESIS EXAMPLE 4 Preparation ofa-4-Bis(n-butylimidoperyleneimido)methylbenzene (Formula 1, R andR=n-butyl, X-Y=a-4-tolyl)

A mixture of n-butylimidoperylene monoanhydride (Formula 2, R=n-butyl;2.46 grams, 0.0055 mole) and 4-aminobenzylamine (0.305 gram, 0.00250mole) and zinc acetate dihydrate (0.44 gram, 0.0020 mole) in 100milliliters of NMP was stirred at room temperature, about 25° C., for 30minutes. The resulting mixture was then heated at reflux for 45 minutes,was cooled to 155° C., and was then filtered through a preheated glassfiber filter. The solid product was washed with 4×30 millilitersportions of boiling DMF, then with 20 milliliters of cold DMF and 2×20milliliters portions of methanol. Drying at 60° C. provided 2.20 gramsof a black solid product ofa-4-bis(n-butylimidoperyleneimido)methylbenzene (Formula 1, R=n-butyl,X-Y=a-4-tolyl), (91 percent yield). A spot test for the presence ofstarting monoanhydride was negative.

SYNTHESIS EXAMPLE 5 Preparation ofb-4-Bis(n-pentylimidoperyleneimido)ethylbenzene (Formula 1, R andR=n-pentyl, X-Y=b-4-ethylbenzene)

A mixture of n-pentylimidoperylene monoanhydride (Formula 2, R=n-pentyl;2.54 grams, 0.0055 mole), b-(4-amino)phenethylamine (0.341 gram, 0.329milliliter, 0.00250 mole) and zinc acetate dihydrate (0.55 gram, 0.0025mole) in 100 milliliters of NMP was stirred at room temperature for 30minutes, followed by heating at reflux for 1.75 hours. The resultantreddish brown suspension was cooled to 150° C., filtered and washed asin Example 4. Drying at 60° C. provided 2.3 grams (90 percent) of theabove reddish brown solid product ofb-4-bis(n-pentylimidoperyleneimido)ethylbenzene (Formula 1, R=n-pentyl,X-Y=b-4-ethylbenzene). A spot test for starting monoanhydride reactantwas negative.

SYNTHESIS EXAMPLE 6 Preparation of4,4'-Bis(n-propylimidoperyleneimido)benzanilide (Formula 1, R andR=n-propyl, X-Y=benzanilide-4,4'-diyl)

Propylimidoperylene monoanhydride (4.76 grams, 0.011 mole),4,4'-diaminobenzanilide (1.135 grams, 0.0050 mole) and zinc acetatedihydrate (1.1 grams, 0.0050 mole) were stirred and heated to reflux in200 milliliters of NMP. After 2.33 hours, the mixture was cooled to 150°C. and was filtered through an 11 centimeter glass fiber filter (WhatmanGrade GF/F) which had been preheated with 50 milliliters of boiling DMF.The solid product was washed in the funnel with 5×50 milliliter portionsof boiling DMF then with 50 milliliters of cold DMF, and 2×25milliliters of water. The resulting wet cake was stirred in 300milliliters of 3 percent aqueous hydrochloric acid for 2 hours at 60° C.The resultant dispersion was filtered and the solid product was washedwith 4×100 milliliter portions of water, then was dried at 60° C. toprovide 3.9 grams (74 percent) of the above orange solid product. A spottest indicated that there was no residual starting monoimide in thisproduct.

SYNTHESIS EXAMPLE 7 Preparation of3,4'-Bis(n-pentylimidoperyleneimido)diphenyl ether (Formula 1, R andR=n-pentyl, X-Y=diphenyl ether-3,4"-diyl)

A mixture of n-pentylimidoperylene monoanhydride (Formula 2, R=n-Pentyl;5.07 grams, 0.011 mole), 3,4'-diaminophenyl ether (1.00 gram, 0.0050mole) and zinc acetate dihydrate (1.1 grams, 0.005 mole) in 200milliliters of NMP was stirred and heated to reflux under argon. After3.33 hours at reflux the dark brown reaction mixture was cooled to 160°C., was filtered and washed with boiling DMF then water, and thentreated with 3 percent aqueous hydrochloric acid in the same manner asExample 6. The product resulting above was dried at 60° C. to provide4.9 grams (90 percent) to provide as a dull red powder.

COMPARATIVE SYNTHESIS EXAMPLE 1 A MONOMERIC PERYLENE BISIMIDEPreparation of N,N'-Bis(n-pentyl)perylene-3,4,9,10-tetracarboxylicdiimide (Formula 3a, Both Rs=n-pentyl)

A mixture of 3,4,9,10-perylenetetracarboxylic dianhydride (3.92 grams,0.010 mole) and n-pentylamine (4.5 grams, 0.060 mole) in 200 millilitersof NMP was stirred and heated to reflux. After 1/2 hour at reflux theresulting dark brown solution was cooled to 150° C. and the suspensionwas filtered through a preheated sintered glass funnel. The solidproduct resulting was washed in the funnel with 3×100 milliliters ofboiling DMF then with 50 milliliters of cold DMF and 2×25 milliliters ofmethanol. The solid product was dried at 60° C. to provide 2.8 grams (56percent) of the above product compound as dark brown light fluffycrystals.

COMPARATIVE SYNTHESIS EXAMPLE 2 A SYMMETRICAL PERYLENE BISIMIDE DIMERPreparation of 1,6-Bis(n-pentylimidoperyleneimido)hexane (Formula 1, Rand R=n-pentyl, X-Y=1,6-hexamethylene)

Pentylimidoperylene monoanhydride (Formula 2, R=n-pentyl; 2.40 grams,0.0050 mole) and 1,6-diaminohexane (0.232 grams, 0.0020 mole) werestirred in 100 milliliters of NMP for 1 hour at room temperature. Themixture was then heated to reflux (202° C.) for 3 hours, was cooled to150° C., and was then filtered through a preheated 9 centimeter glassfiber filter (Whatman Grade GF/F). The solid product was then washedwith 3×100 milliliter portions of boiling DMF, then with 50 millilitersof cold DMF, followed by 2×25 milliliter portions of 5 percent aqueouspotassium hydroxide and finally with 4×25 milliliters of water. Theproduct was dried at 60° C. to provide 2.0 grams (97 percent) of theabove symmetrical dimer product as a dark brown solid.

Preparation of Dispersions of Unsymmetrical Perylene Bisimide Dimers inPoly(vinyl acetate)

To demonstrate the application of the invention unsymmetrical dimers asdispersed colorants, sample of pigments dispersed in poly(vinyl acetate)were prepared as follows: 0.2 gram of perylene pigment, 8 milliliters ofa 1.5 percent W/W solution of poly(vinyl acetate) (M_(w) =45,000;Polysciences, Inc.) in dichloromethane and 70 grams of 1/8 inch diameterstainless balls were charged into a 30 milliliter glass jar. The jar wassealed and the mixture was milled on a roll mill for 3 to 5 days untilthe pigment particles were submicron, below 1 micron in diameter size,and were finely dispersed. Colored films were prepared by coating aclear plastic sheet, such as MYLAR® polyester with the dispersion usinga #8 wire-wound rod. The nominal film wet thickness was about 20microns, and the dried film was about 1 micron. The films, comprised ofabout 60 percent of well-dispersed pigment in PVA, had an opticaldensity of about 1 and exhibited a variety of colors.

The large range of colors available by varying the R and X-Y groups ofthe unsymmetrical dimers of this invention is illustrated in Table 1,and which table provides the color of films prepared from fiverepresentative compounds.

                  TABLE 1                                                         ______________________________________                                        Colors of Raw Pigments And PVA-Dispersed Films of Some                        Unsymmetrical Perylene Bisimide Dimers                                                              Color of Raw                                                                              Color of PVA                                R      X-Y            Pigment     Dispersion                                  ______________________________________                                        n-propyl                                                                             a-4-tolyl      black       brown                                       n-propyl                                                                             b-4-phenethyl  red-brown   red                                         n-pentyl                                                                             2-methyl-1,5-  brown       red-brown                                          pentamethylene                                                         n-butyl                                                                              benzanilide-4,4'-diyl                                                                        red-brown   orange                                      n-pentyl                                                                             diphenyl ether-3,4'-diyl                                                                     red         magenta                                     ______________________________________                                    

Xerographic Evaluation of Unsymmetrical Perylene Bisimide Dimers

Photoresponsive imaging members were fabricated with the unsymmetricalperylene dimer pigments obtained by Synthesis Examples 1, 3, 4, 5 and 7,respectively, and from the Comparative Synthesis Examples 1 and 2,representing the monomeric perylene bisimide and the symmetricalbisimide dimer corresponding to Synthesis Example 2. Thesephotoresponsive, or photoconductive imaging members are generally knownas dual layer photoreceptors containing a photogenerator layer, andthereover a charge transport layer. The photogenerator layer wasprepared from a pigment dispersion as follows: 0.2 gram of the perylenedimer pigment was mixed with 0.05 gram of polyvinylcarbazole (PVK)polymer and 8.1 milliliters of methylene chloride in a 30 milliliterglass bottle containing 70 grams of 1/8-inch stainless steel balls. Thebottle was placed on a roller mill and the dispersion was milled for 4days. Using a film applicator of 1.5 mil gap, the pigment dispersion wascoated to form the photogenerator layer on a titanized MYLAR® substrateof 75 microns in thickness, which had a gamma amino propyl triethoxysilane layer, 0.1 micron in thickness, thereover, and E. I. DuPont49,000 polyester adhesive thereon in a thickness of 0.1 micron.Thereafter, the photogenerator layer formed was dried in a forced airoven at 135° C. for 20 minutes. Photogenerator layers for each devicewere each overcoated with an amine charge transport layer prepared asfollows. A transport layer solution was made by mixing 8.3 grams ofMAKROLON™, a polycarbonate resin, 4.4 grams ofN,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine and82.3 grams of methylene chloride. The solution was coated onto the abovephotogenerating layer using a film applicator of 10 mil gap. Theresulting members were dried at 135° C. in a forced air oven for 20minutes. The final dried thickness of transport layer was 20 microns.

The xerographic electrical properties of each imaging member were thendetermined by electrostatically charging its surface with a coronadischarging device until the surface potential, as measured by acapacitively coupled probe attached to an electrometer, attained aninitial value V_(o). After resting for 0.5 second in the dark, thecharged member reached a surface potential of V_(ddp), dark developmentpotential, and was then exposed to light from a filtered xenon lamp. Areduction in the surface potential to V_(bg), background potential dueto photodischarge effect, was observed. The dark decay in volt/secondwas calculated as (V_(o) -V_(ddp))/0.5. The lower the dark decay value,the superior is the ability of the member to retain its charge prior toexposure by light. Similarly, the lower the V_(ddp), the poorer is thecharging behavior of the member. The percent photodischarge wascalculated as 100 percent×(V_(ddp) -V_(bg))/V_(ddp). The light energyused to photodischarge the imaging member during the exposure step wasmeasured with a light meter. The photosensitivity of the imaging membercan be described in terms of E_(1/2), amount of exposure energy inerg/cm² required to achieve 50 percent photodischarge from the darkdevelopment potential. The higher the photosensitivity, the smaller theE_(1/2) value. High photosensitivity (lower E_(1/2) value), lower darkdecay and high charging are desired for the improved performance ofxerographic imaging members.

The following Table 2 summarizes the xerographic electrical results whenthe exposed light used was at a wavelength of 500 nanometers.

                  TABLE 2                                                         ______________________________________                                        Imaging                          Dark                                         Member                                                                              Perylene         Synthesis Decay E.sub.1/2                              No.   Dimer            Example   V/s   erg/cm.sup.2                           ______________________________________                                        1     1,5-Bis(n-       1         27.6  8.0                                          butylimidoperyleneimido)-2-                                                   methylpentane                                                           2     1,5-Bis(n-       2         35.8  4.3                                          pentylimidoperyleneimido)-2-                                                  methylpentane                                                           3     a-4-Bis(n-       4         15.8  19                                           butylimidoperyleneimido)                                                      toluene                                                                 4     b-4-Bis(n-       5         31    14                                           pentylimidoperyleneimido)                                                     ethylbenzene                                                            5     3,4'-Bis(n-      7         34.6  7.6                                          pentylimidoperyleneimido)                                                     diphenyl ether                                                          6     N,N'-Bis(n-pentyl)perylene-                                                                    Comparative                                                                             1.2   6.7                                          3,4,9,10-tetracarboxylic acid                                                                  Synthesis                                                    dicarboximide    Example 1                                              7     1,6-Bis(n-       Comparative                                                                             49.4  8.9                                          pentylimidoperyleneimido)                                                                      Synthesis                                                    hexane           Example 2                                              ______________________________________                                    

All the imaging members with the invention unsymmetrical photogeneratingpigments exhibited acceptable charge acceptance, and most showed low tomoderate dark decay ranging from about 20 to <50 volts per second, andphotosensitivities ranging from excellent (E_(1/2) of about 4.3ergs/cm²) to moderate (E_(1/2) of about 19 ergs/cm²) indicating thatthese unsymmetrical perylene dimers would be very useful for xerographicimaging applications. There does not appear to be an empirical ortheoretical correlation between the chemical structures of the perylenepigments and their efficacies as photogenerator pigments for xerographicimaging applications. However, the much higher sensitivity (E_(1/2) =4.3ergs/cm²) observed for the unsymmetrical dimer of Example 2, compared tothe related n-pentyl monomeric perylene bisimide of Comparative Example1 (E_(1/2) =6.7) and the related symmetrical dimer of ComparativeExample 2 (E_(1/2) =8.9), which has a 6-carbon symmetrical bridginggroup instead of the unsymmetrical 6-carbon bridge of Example 2,indicates that the unsymmetrical dimers of this invention possess uniquexerographic electrical properties.

Other embodiments and modifications of the present invention may occurto those skilled in the art subsequent to a review of the informationpresented herein; these embodiments, modifications, and equivalentsthereof, are also included within the scope of the present invention.

What is claimed is:
 1. Photoconductive imaging members comprised ofunsymmetrical dimeric perylene as a charge generator, wherein saidperylene is of the following formula ##STR7## wherein R is hydrogen,alkyl, cycloalkyl, substituted alkyl, aryl, substituted aryl, aralkyl orsubstituted aralkyl group, and X-Y is an unsymmetrical bridging moietyof alkylene, substituted alkylene, arylene, substituted arylene,aralkylene or substituted aralkylene.
 2. A photoconductive imagingmember comprised of a supporting substrate, a photogenerator layercomprised of an unsymmetrical perylene bisimide photogenerator pigmentas essentially represented by the formula ##STR8## wherein R ishydrogen, alkyl, cycloalkyl, substituted alkyl, aryl, substituted aryl,aralkyl or a substituted aralkyl group, and X-Y is an unsymmetricalbridging moiety of alkylene, substituted alkylene, arylene, substitutedarylene, aralkylene or substituted aralkylene.
 3. An imaging member inaccordance with claim 2 wherein R is hydrogen.
 4. An imaging member inaccordance with claim 2 wherein alkyl contains from 1 to about 25 carbonatoms, aryl contains from 6 to about 24 carbon atoms, and aralkylcontains from 7 to about 30 carbon atoms.
 5. An imaging member inaccordance with claim 2 wherein alkyl is methyl, ethyl, propyl,isopropyl, butyl, isobutyl, sec-butyl, 2-methylbutyl, 3-methylbutyl,n-pentyl, 2-pentyl, 3-pentyl, neopentyl, n-hexyl, n-heptyl, n-octyl,n-nonyl or n-decyl.
 6. An imaging member in accordance with claim 2wherein cycloalkyl is cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl,cycloheptyl, cyclooctyl or cyclododecyl, and wherein substituted alkylis 3-hydroxypropyl, 2-methoxyethyl, 3-methoxypropyl, 3-ethoxypropyl,4-methoxybutyl, 2-carboxyethyl, 3-carboxybutyl or 3-dimethylaminopropyl.7. An imaging member in accordance with claim 2 wherein aryl is phenyl,2-, 3-, or 4-phenylphenyl, or 1- or 2-naphthyl.
 8. An imaging member inaccordance with claim 2 wherein substituted aryl is 2-, 3-, or4-hydroxyphenyl, 2-, 3-, or 4-methylpheny, 2-, 3-, or4-tertiary-butylphenyl, 2-, 3-, or 4-methoxyphenyl, 2-, 3-, or4-halophenyl, 2-, 3-, or 4-nitrophenyl, 2-, 3-, or 4-cyanophenyl or 2-,3-, or 4-dimethylaminophenyl.
 9. An imaging member in accordance withclaim 2 wherein aralkyl is benzyl, phenethyl or 3-phenylpropyl.
 10. Animaging member in accordance with claim 2 wherein substituted aralkyl is2-, 3-, or 4-hydroxybenzyl, 2-, 3-, or 4-methylbenzyl, 2-, 3-, or4-tertiary-butylbenzyl, 2-, 3-, or 4-methoxybenzyl, 2-, 3-, or4-halobenzyl, 2-, 3-, or 4-nitrobenzyl, 2-, 3-, or 4-cyanophenyl, 2-,3-, or 4-dimethylaminobenzyl, 2-, 3-, or 4-hydroxyphenethyl, 2-, 3-, or4-methylphenethyl, 2-, 3-, or 4-tertiary-butylphenethyl, 2-, 3-, or4-methoxyphenethyl, 2-, 3-, 4-halophenethyl, 2-, 3-, or4-nitrophenethyl, 2-, 3-, or 4-cyanophenethyl or 2-, 3-, or4-dimethylaminophenethyl, and wherein halo is chloro, fluoro, iodo, orbromo.
 11. An imaging member in accordance with claim 2 wherein alkylenecontains from 3 to about 20 carbon atoms and arylene contains from 6 toabout 24 carbon atoms.
 12. An imaging member in accordance with claim 2wherein alkylkene is 1,2-propylene, butane-1,2-diyl, butane-1,3-diyl,pentane-1,3-diyl, pentane-1,4-diyl, 2-methylbutane-1,4-diyl,hexane-1,5-diyl, or 2-methylpentane-1,5-diyl.
 13. An imaging member inaccordance with claim 2 wherein alkylene is substituted2-methoxybutane-1,4-diyl, 2-hydroxybutane-1,4-diyl or2-dimethylaminobutane-1,4-diyl.
 14. An imaging member in accordance withclaim 2 wherein arylene is biphenyl-2,3-diyl, biphenyl-2,4'-diyl,biphenyl-1,4-diyl, naphthalene-1,3-diyl, naphthalene-1,6-diyl ornaphthalene-1,7-diyl, wherein arylene is substituted 2-fluoro-,2-chloro-, 2-bromo-, 2-hydroxy-, 2-methyl-, 2-methoxy-,2-dimethylamino-,2-cyano-, or 2-nitro-phenyl, 2-fluoro-, 2-chloro-, 2-bromo-, 2-hydroxy-,2-methyl-, 2-methoxy-, 2-dimethylamino-, 2-cyano-, or 2-nitro-biphenylor 3-fluoro-, 3-chloro-, 3-bromo-, 3-hydroxy-, 3-methyl-, 3-methoxy-,3-dimethylamino-, 3-cyano-, or 3-nitro-biphenyl, diphenylether-3,4'-diyl, diphenylsulfone-3,4'-diyl or benzanilide-4,4'-diyl. 15.An imaging member in accordance with claim 2 wherein aralkylene istoluene-a,3-diyl, toluene-a,4-diyl, ethylbenzene-4-diyl,propylbenzene-g,4-diyl, fluorene-2,9-diyl or fluorene-3,9-diyl.
 16. Animaging member in accordance with claim 2 wherein substituted aralkyleneis 2-fluoro-, 2-chloro-, 2-bromo-, 2-hydroxy-,2-methyl-, 2-methoxy-,2-dimethylamino-, 2-cyano- or 2-nitro-toluene-a,4-diyl, 2-fluoro-,2-chloro-, 2-bromo-, 2-hydroxy-, 2-methyl-, 2-methoxy-,2-dimethylamino-, 2-cyano- or 2-nitro-ethylbenzene-b,4-diyl, or3-fluoro-, 3-chloro-, 3-bromo-, 3-hydroxy-, 3-methyl-, 3-methoxy-,3-dimethylamino-, 3-cyano- or 3-nitro-ethylbenzene-b,4-diyl.
 17. Animaging member in accordance with claim 2 wherein X-Y is 1,2-propylene,butane-1,2-diyl, butane-1,3-diyl, pentane-1,3-diyl, pentane-1,4-diyl,2-methylbutane-1,4-diyl, hexane-1,5-diyl, or 2-methylpentane-1,5-diyl.18. An imaging member in accordance with claim 2 wherein R is methyl,ethyl, n-propyl, 3-methoxypropyl, n-butyl, isobutyl, n-pentyl, 2-pentyl,3-pentyl, 2-methylbutyl, 3-methylbutyl, neopentyl, n-hexyl, n-heptyl,n-octyl, benzyl, 3-chlorobenzyl or phenethyl.
 19. An imaging member inaccordance with claim 2 wherein R is methyl, ethyl, n-propyl,3-methoxypropyl, n-butyl, isobutyl, n-pentyl, 2-pentyl, 3-pentyl,2-methylbutyl, 3-methylbutyl, neopentyl, n-hexyl, n-heptyl, n-octyl,benzyl, 3-chlorobenzyl or phenethyl, and X-Y is 1,2-propylene,butane-1,2-diyl, butane-1,3-diyl, pentane-1,3-diyl, pentane-1,4-diyl,2-methylbutane-1,4-diyl, hexane-1,5-diyl, or 2-methylpentane-1,5-diyl.20. An imaging member in accordance with claim 2 wherein R is hydrogen,methyl, ethyl, n-propyl, 3-methoxypropyl, n-butyl, isobutyl, n-pentyl,2-pentyl, 3-pentyl, 2-methylbutyl, 3-methylbutyl, neopentyl, n-hexyl,n-heptyl, n-octyl, benzyl, 3-chlorobenzyl or phenethyl, and X-Y istoluene-a,4-diyl, or X-Y is ethylbenzene-b,4-diyl; or wherein R ishydrogen, methyl, ethyl, n-propyl, 3-methoxypropyl, n-butyl, isobutyl,n-pentyl, 2-pentyl, 3-pentyl, 2-methylbutyl, 3-methylbutyl, neopentyl,n-hexyl, n-heptyl, n-octyl, benzyl, 3-chlorobenzyl or phenethyl, and X-Yis diphenyl ether-3,4'-diyl; or wherein R is hydrogen, methyl, ethyl,n-propyl, 3-methoxypropyl, n-butyl, isobutyl, n-pentyl, 2-pentyl,3-pentyl, 2-methylbutyl, 3-methylbutyl, neopentyl, n-hexyl, n-heptyl,n-octyl, benzyl, 3-chlorobenzyl or phenethyl, and X-Y isbenzanilide-4,4'-diyl.
 21. An imaging member in accordance with claim 2wherein R is n-pentyl, and X-Y is 2-methylpentane-1,5-diyl.
 22. Animaging member in accordance with claim 2 wherein the supportingsubstrate is a metal, a conductive polymer composition, or an insulatingpolymer with a thickness of from about 30 microns to 300 micronsoptionally overcoated with an electrically conductive layer with athickness of from about 0.01 micron to 1 micron.
 23. An imaging memberin accordance with claim 2 wherein the supporting substrate is comprisedof aluminum, and there is further included an overcoating top layer onsaid member comprised of a polymer.
 24. An imaging member in accordancewith claim 2 wherein the unsymmetrical dimer photogenerator pigment isdispersed in a resinous binder in an amount of from about 5 percent toabout 95 percent by weight.
 25. An imaging member in accordance withclaim 23 wherein the resinous binder is a polyester, apolyvinylcarbazole, a polyvinylbutyral, a polycarbonate, apolyethercarbonate, an aryl amine polymer, a styrene copolymer, or aphenoxy resin.
 26. An imaging member in accordance with claim 2 whereinthere is further included a charge transport layer selected from thegroup consisting of aryl amines or aryl amine polymers.
 27. An imagingmember in accordance with claim 2 wherein there is further included acharge transport layer comprised of aryl amine molecules dispersed in ahighly insulating polymer in an amount of from about 20 to 60 percent,and preferably from 30 to 50 percent, wherein X is an alkyl group or ahalogen.
 28. An imaging member in accordance with claim 27 wherein thehighly insulating polymer is a polycarbonate, a polyester, or a vinylpolymer.
 29. An imaging member in accordance with claim 2 wherein thephotogenerating layer is of a thickness of from about 0.2 to about 10microns, wherein there is further included the charge transport layer isof a thickness of from about 10 to about 100 microns, wherein asupporting substrate is overcoated with a polymeric adhesive layer of apolyester of a thickness of from about 0.01 to about 1 micron, andwherein the charge transport layer is situated between the supportingsubstrate and the photogenerator layer.
 30. An imaging member inaccordance with claim 2 wherein R is hydrogen, methyl, ethyl, n-propyl,3-methoxypropyl, n-butyl, isobutyl, n-pentyl, 2-pentyl, 3-pentyl,2-methylbutyl, 3-methylbutyl, neopentyl, n-hexyl, n-heptyl, n-octyl,benzyl, 3-chlorobenzyl or phenethyl, and X-Y is toluene-a,4-diyl,ethylbenzene-b,4-diyl, diphenyl ether-3,4'-diyl, orbenzanilide-4,4'-diyl.
 31. An imaging method which comprises theformation of a latent image on the photoconductive imaging member ofclaim 2, developing the image with a toner composition comprised ofresin and pigment, transferring the image to a substrate and fixing theimage thereto.